In a known seat device, a seat position is adjustable in a fore-aft direction relative to a vehicle floor by an operation of a seat sliding device for using a space in a vehicle room for various purposes, for example, for accommodating occupants, or loading luggage. Normally, the seat position in a fore-aft direction is divided into a seating range and a non-seating range. The seating range is defined that a seat is moved to a rear part of the vehicle room and an occupant can sit down on the seat. The non-seating range is defined that the seat is moved forward to extend a loading space for luggage. When the seat is at the seating range, a position of a seat belt attached to a vehicle body and a position of the occupant is set properly, and a seatback is set at a proper space around the occupant. Meanwhile, when the seat is positioned at the non-seating range, the seatback or a seat cushion is folded for the occupant not to sit down on the seatback or the seat cushion. Thus, the occupant is protected from improper use of the seat at a position where the occupant can not use the seat belt properly. The known seat device is described, for example, in Japanese Patent Publication No. 3284901.
In order to achieve the function stated above, the known seat device includes a stopper mechanism which is configured to be released when a seat cushion is tipped up so that an occupant can not sit down on, to move the seat from a seating range to a non-seating range. However, when the occupant is not accustomed to an operation of the seat device, and improperly moves the seat for loading the luggage without tipping the seat cushion up, the stopper mechanism likely to be broken by an applied heavy load. The stopper mechanism has to be strong not to be broken down, which makes the stopper mechanism large and costly. Further, a complex mechanism is required to return a state of the stopper mechanism when the seat is returned to the seating range.
A need thus exists for a seat device structured simple, and structured that a heavy load is not applied when a seat is moved from a seating range to a non-seating range.